Implantable medical devices for producing a therapeutic result in a patient are well known. Examples of such implantable medical devices include implantable drug infusion pumps, implantable neurostimulators, implantable cardioverters, implantable cardiac pacemakers, implantable defibrillators and cochlear implants. Of course, it is recognized that other implantable medical devices are envisioned which utilize energy delivered or transferred from an external device.
A common element in most of these implantable medical devices is the need for electrical power in the implanted medical device. The implanted medical device typically requires electrical power to perform its therapeutic function whether it be driving an electrical infusion pump, providing an electrical neurostimulation pulse or providing an electrical cardiac stimulation pulse. This electrical power is derived from a power source.
Typically, a power source for an implantable medical device is a rechargeable power source such as rechargeable batteries and, in particular, lithium ion batteries. Such batteries can have a capacity which is exhausted much earlier than the useful life of the implantable medical device. Electrical power can be transcutaneously transferred to the implanted medical device to recharge the rechargeable batteries through the use of inductive coupling. An external power source temporarily positioned on the surface of the skin of the patient can recharge the implanted medical device's batteries. In fact, many systems and methods have been used for transcutaneously inductively recharging a rechargeable power source used in an implantable medical device.
Transcutaneous energy transfer through the use of inductive coupling involves the placement of two coils positioned in close proximity to each other on opposite sides of the cutaneous boundary. The internal coil, or secondary coil, is part of or otherwise electrically associated with the implanted medical device. The external coil, or primary coil, is associated with the external power source or external charger, or recharger. The primary coil is driven with an alternating current. A current is induced in the secondary coil through inductive coupling. This current can then be used to charge, or recharge, an internal power source.